\section{Material and methods}

	\subsection{Biologicial matérial}

		\subsubsection{Youg trees in greenhouse}

This study was led on 50 \sa one and two years old (2 $\times$ 25 trees). These trees were collected in forest one or two years ago in the seedling state and have grows up since in jar. At the beginning of the experiment trees have been transferred in bigger new jars. Some new soil comes to complete the soil in which trees grew before.

		\subsubsection{Adult trees in forest}

In complement 15 others \sa older and bigger than greenhouse ones but unknown ages were choosen in forest. The evaluation of tree ages is impossible in tropical rain forest because of absence of growth ring. We can't have a controlled plantation of big trees in a greenhouse. So, we chooses trees in forest big enough and tall enough to be sure they are very older than the ones in greenhouse.

	\subsection{Tree stress traitements}
	
			\subsubsection{Youg trees in greenhouse}

 Following \citet{Yoshida2000, Jaouen2007} or \citet{Coutand2014}, the young plantations were tilted and staked artificially (\Fig{inclin simarouba}) according to 5 angles $\theta$: 0\textdegree, 20\textdegree, 40\textdegree, 60\textdegree and 80\textdegree . The pole fixation allows to maintain a controlled gravitational stimulus constant in the time and uniform in the space.
 
The protocol is the following ones: 5 trees of 1 year tilted and staked according to 5 angles and 5 trees of 2 years tilted and stacked according to the same 5 angles. The whole is repeated 5 times for a total of 50 trees. Trees are then kept growing bewteen 50 and 85 days. With the pole fixation trees were not able to recover (\Fig{inclinb}).  When the fixation released at the end of experiment, the saplings sprang upward. \citet{Yoshida2000} named this as the “spring-back” phenomenon. It is induced by the release of the growth stress that has built up during the growing season.

\begin{figure}[h]
	\centering
	\footnotesize	
	\subfloat[Stacked tree on day 0]
	{
		\def\svgwidth{0.21\textwidth}
		\input{img/simarouba_vectorized2.pdf_tex}
		\label{inclinb}
	}
	\qquad
	\subfloat[Spring-back effect]
	{
		\includegraphics[width=0.142\textwidth]{img/simarouba_vectorized3.pdf}
		\label{inclinc}
	}
	\caption{shematic representation of the experiment on young \sa{} -- (a) during the experiment tree are tilted and attached with a pole; (b) at the end of experiment when the fixation is released, the sapling sprang upward; Red points labelled with the $\diameter$	symbol are the points were the diameters have been measured and were the anatomical observations have been made.}
	\label{inclin simarouba}
\end{figure}

		\subsubsection{Adult trees in forest}

The 15 trees from forest were tilted artificially but not stacked because of the impossibility to stack big trees. They were guying and tilted with an angle of approximately 40\textdegree. In this case the stimulus is not controlled neighter in time nor in space. Trees are free to right up. Origins of trees are unknown.

	\subsection{Counting the data}
	
		\subsubsection{Youg trees in greenhouse}
		
Data have been counting from the 50\textsuperscript{th} to the 85\textsuperscript{th} days. Each week a set of 10 trees is used and prepared for observations. Diameters are measured on the three points (see. \Fig{inclin simarouba}). On each point a piece of trunk (2 cm length) is taken and kept in water.
		
		\subsubsection{Adult trees in forest}
		
Je ne sais pas encore
		
	\subsection{Anatomical observations}
	
		\subsubsection{Youg trees in greenhouse}

Trees have been cutted according to their transverse section at the level of marked places to make anatomical shape about 20~µm with a manual microtome. Cuttings are then colored with Safranin and Alcian blue. This stage allows to color lignified tissues in red and not lignified tissues (i.e. the tension wood with \gl) in blue). This stage allows (i) to confirm the absence or the presence of \gl in the optical microscope (ii). 

		\subsubsection{Adult trees in forest}
		
Je ne sais pas trop